There is considerable interest in ion-implantation doping of GaAs and InP, especially for microwave uses. Ion-Implantation is considered to be an alternative to diffusion for the creation of a heavily doped thin region beneath the surface of the seimconductor material. Heat treating GaAs or InP is necessary after most ion-implantations for two purposes: (1) to increase the electrical activity of the implanted ions; and (2) to remove the lattice damage caused in the material by the ions during their implantation.
It has been learned that ion-implanted semiconductors during annealing undergo incongruent evaporation at temperatures lower than their annealing temperatures. Therefore, it is now standard practice to encapsulate the semiconductors with suitable dielectric layers during annealing, or to anneal the semiconductors in a carefully controlled environment to prevent evaporation from their surfaces. In all cases, the goal has been to develop an annealing process which preserves the chemical and electrical properties of the implanted material during high temperature annealing, while providing high mobility and activation of the implanted semiconductor material.
Prior methods of annealing smooth surfaces of ion-implanted GaAs or InP have often involved a step of depositing a dielectric encapsulating film of thermal matching characteristics on the implanted surface, and removing it after annealing.